ABSTRACT: Laramide Left-Slip Evolution and Tectonic Implications of the North Owl Creek Fault System, Wyoming

PAYLOR, EARNEST D., II, Jet Propulsion Laboratory, Pasadena, CA, and AN YIN, University of California-Los Angeles, Los Angeles, CA

Structures transverse to the regional shortening direction are not uncommon in regions of contractional deformation. Their recognition, however, is critical particularly for constructing balanced cross sections and estimating shortening. Systematic mapping and kinematic analysis reveal that the east-striking North Owl Creek fault system, central Wyoming, is such a transverse structure. The main component of this system, the east-striking North Owl Creek fault, is high-angle, left-slip and links with (does not crosscut) northwest-trending contractional structures along its trace. The magnitude of left slip along the North Owl Creek fault is estimated to be a minimum of 4 km based on differential shortening on each side of the fault in the western Owl Creek Mountains; however, displacem nt increases westward. Vertical separation, measured on top of the Precambrian basement, varies from 10s to 1000s of meters, and changes from south-side up to north-side up toward the west. Kinematic data reveal the dominant regional shortening direction is approximately east-northeast-west-southwest. The transverse system is interpreted to have accommodated differential shortening between the Washakie thrust system and the west Owl Creek Mountains fault system during Laramide deformation. It evolved by the propagation and subsequent interaction of lateral ramps, one linking the west-southwest-directed Black Mountain thrust, and the other linking the east-northeast-directed Mud Creek thrust. The interpretation explains the general lack of systematic crosscutting relations and the kinemat c compatibility between northwest- and east-trending structures in this region. In addition, it predicts a protracted deformational history for the fault system with systematic initiation and subsequent coeval development of structures. Such a model may be applicable to other east-striking Laramide-aged fault systems in central Wyoming, including those associated with the eastern Owl Creek and Granite Mountains.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)